[1] ARHANGEL'SKII A. V., ISLER R., TIRONI G.: 
On pseudo-radial spaces. Comment. Math. Univ. Carolinae 27 (1986) 137-154. 
MR 0843426[2] M. BELL J. GINSBURG G. WOODS: 
Cardinal inequalities for topological spaces involving the weak Lindelöf numbers. Pac. J. Math. 29 (1978), 37-45. 
MR 0526665[3] BELLA A.: 
Free sequences in pseudo-radial spaces. Comment. Math. Univ. Carolinae 27 (1986), 163-170. 
MR 0843428 | 
Zbl 0596.54006[5] BELLA A.: 
Some remarks on set tightness in pseudo-radial spaces. preprint. 
MR 0932442[7] JUHÁSZ I.: 
Cardinal functions in topology. Math. Centre Tracts, 34, Amsterdam, 1971. 
MR 0340021[8] JUHÁSZ I.: Variations on tightness, Topology and its applications. Fourth Int. Conf. Dubrovnik, Sept. 30-Oct. 5, 1985. Abstracts.
[9] MALYHIN V. I.: 
On tightness and Suslin number in exp X and in a product of spaces. Soviet Math. Dokl. 13, 2 (1972). 
MR 0300241 | 
Zbl 0257.54004